A variety of batteries employ a stack of electrodes having anodes alternating with cathodes. These electrode stacks can employ bags constructed of a separator material. Typically, the cathodes in the stack are positioned in a separator bag while the anodes are not positioned in separator bags. This arrangement places the separator between adjacent anodes and cathodes.
The separator bags can be formed by bonding edges of the separator material together so as to form an envelope. The sides are bonded together using welds or mechanical seals to form seams that bring one side of the separator bag into contact with another side of the separator bag. An electrode is inserted into the bag such that edges of the electrode are adjacent to the seams of the bag. Because the electrode is thicker than the seams, the bag is pinched together adjacent to the edges of the electrode. This pinching can cause wrinkles to develop in the separator bag. The wrinkles can cause lithium dendrite formation and can accordingly affect battery performance. As a result, there is a need for an improved separator bag.